Drop the index hint from the auto-postpone sweep

app/models/card/entropic.rb

@@ -21,18 +21,10 @@ module Card::Entropic
     # queries with a single constant cutoff, so `account_id = ? AND
     # last_active_at <= ?` rides the existing index instead of computing the
     # threshold per row across every card in the system.
-    #
-    # The account+board+status index is pinned with use_index so this background
-    # sweep's plan is independent of InnoDB statistics freshness: for a large
-    # account's selective board group the optimizer can otherwise flip to an
-    # account-wide scan when stats go stale, turning a ~30ms query into a
-    # multi-second one. Pinning caps the tail; the negligible cost on broad
-    # board groups is irrelevant for a background job.
     def auto_postpone_all_due(as_of: Time.now)
       Account.find_each do |account|
         account.boards.includes(:entropy).group_by(&:auto_postpone_period).each do |period, boards|
           account.cards.active
-            .use_index(:index_cards_on_account_id_and_board_id_and_status)
             .where(board_id: boards.map(&:id))
             .where(last_active_at: ..(as_of - period))
             .find_each do |card|